1. Field of the Invention
The present invention is generally in the field of semiconductor fabrication and packaging. More particularly, the present invention is in the field of voltage regulation for semiconductor dies.
2. Related Art
One role of a voltage regulator is to generate a stable and desired output voltage from a source that may be fluctuating or is otherwise unsuitable for a target device or circuitry. As is known in the art, a typical voltage regulator has an input terminal supplied with a power supply, an output terminal for providing a desired output voltage to the target device or circuitry and a reference input which, through a feedback mechanism, monitors the output voltage of the voltage regulator and ensures that the output is appropriate for the target device or circuitry. As an example, a voltage regulator can convert a 3.3 volt external power supply into a 1.8 volt internal supply for use in a semiconductor chip""s internal or core circuitry.
Structure 100 in FIG. 1 shows a conventional approach wherein a voltage regulator is situated inside the die to generate a steady and desired voltage for the die""s core circuitry. As shown in FIG. 1, semiconductor die (xe2x80x9cdiexe2x80x9d) 120 is attached to substrate 116, which is mounted on printed circuit board (xe2x80x9cPCBxe2x80x9d) 140. Die 120 has bond pads, e.g. bond pad 130, which serve as means by which die 120 can be electrically connected to PCB 140 or to other devices on PCB 140 by way of bond wires and leads (not shown) in a manner known in the art. Bond pads on die 120 can be, for example, I/O pads interfacing with external devices or Vdd pads supplying power to the core. Die 120 further comprises voltage regulator 110, which in the present example is a 3.3V-to-1.8V regulator, meaning that voltage regulator 110 converts a 3.3 volt supply to a 1.8 volt supply required for the core circuitry of die 120. The source of the 3.3 volt supply can be, for example, an external power supply.
The conventional packaging approach illustrated in FIG. 1 wherein voltage regulator 110 is on die 120 has several disadvantages. One disadvantage of such an on-die approach is the loss of die area. Voltage regulators are typically in the range of 300 microns by 400 microns and thus take up valuable die area that could be utilized more constructively.
Another disadvantage of the conventional packaging approach illustrated in FIG. 1 relates to manufacturing costs. As is known in the art, voltage regulators can be fabricated utilizing relatively inexpensive processes, for example a 0.25 micron CMOS process. However, when the voltage regulator is fabricated on-die, the processing of the voltage regulator is necessarily tied to the processing of the die itself. Thus, if the die is fabricated utilizing a relatively more expensive process, for example a silicon-germanium process, the production cost for the voltage regulator is raised concomitantly.
A further disadvantage of the conventional approach illustrated in FIG. 1 is the susceptibility of an on-die voltage regulator, such as voltage regulator 110 on die 120, to noise produced by the die. Noise from the die can impair the voltage regulator""s ability to generate a stable and desired output voltage. More specifically, the reference voltage at the voltage regulator""s reference terminal can fluctuate due to the noise. As a result, the accuracy of the reference is compromised and the voltage regulator""s output voltage is destabilized. Manifestly, the voltage supplied to the die""s core circuitry will be likewise unstable.
There is thus a need in the art for an approach for utilizing a voltage regulator which will free up valuable die area, which will be cost effective and which will shield the voltage regulator from noise produced by the die so as to result in superior voltage regulation.
The present invention is directed to voltage regulation for semiconductor dies and related structure. The invention presents an innovative packaging approach wherein a voltage regulator is placed off-die and directly on the packaging substrate.
According to one embodiment, a voltage regulator is placed directly on the packaging substrate. An output of the voltage regulator is a core voltage line that runs adjacent to a die attach area on the packaging substrate. An input of the voltage regulator is typically coupled to a power supply which, in one embodiment, is also an I/O voltage line that runs adjacent to the die attach area on the packaging substrate. In one embodiment, the core voltage line is shaped as a ring encircling the die attach area on the packaging substrate. In another embodiment, the I/O voltage line is also shaped as a ring encircling the die attach area on the packaging substrate.
The I/O voltage line, or the I/O voltage ring as the case may be, provides the voltage regulator with an external power supply from which the voltage regulator produces a steady output voltage on the core voltage line, or the core voltage ring. Further, a semiconductor die having at least one I/O Vdd bond pad and at least one core Vdd bond pad can be mounted in the die attach area. The I/O Vdd bond pad of the semiconductor die can be connected to the I/O voltage ring in a manner known in the art, such as by use of bond wires. Similarly, the core Vdd bond pad of the semiconductor die can be connected to the core voltage ring also in a manner known in the art, such as by use of bond wires.
By placing the voltage regulator off-die, the invention results in superior voltage regulation, since the off-die voltage regulator is not exposed to the noise produced by the digital circuitry of the semiconductor die containing the core. Moreover, the invention results in the freeing up of valuable semiconductor die space for uses related to the core functions. Further, because the voltage regulator is placed off-die, the voltage regulator can be fabricated utilizing a relatively inexpensive process to further reduce production costs.